1. Field of the Invention
The present invention relates, in general, to safety devices, and in particular, to earplugs and earpieces that protect the hearing of a human being.
2. Description of the Prior Art
Plastisol is a composition well-known to those skilled in the art, and "plastisol", as that term is used herein and as known by those skilled in the art, can be defined as follows:
Plastisols . . . in their simplest form, are dispersions of fine-particle-size PVC resins in liquid vehicles consisting of plasticizers, plasticizers plus dilutents, or plasticizers plus solvent and stabilizers. Typical ingredients of commercial plastisols include dispersion resins, blending resins, plasticizers, stabilizers, fillers, pigments, thinners, blowing agents, viscosity modifiers, flame retardants, smoke suppressants, adhesion promoters, release agents, and specialty additives such as UV screeners, air release promoters, and moisture absorbers. PA1 Plastisols are a unique liquid form of "vinyl" compound in the unprocessed state. A plastisol is a suspension of PVC in a liquid plasticizer to produce a fluid mixture which may range in viscosity from a pourable liquid to a heavy paste. This fluid may be spread onto a substrate, poured into a mold, sprayed onto a surface, etc. The plastisol is converted into a homogeneous "vinyl" product through exposure to heat, e.g., 350 degrees F, depending on the specific ingredients used. The heat causes the suspended resin to be "Fused" or dissolved in the plasticizer. Upon cooling, a flexible vinyl product (depending on the recipe used) is formed, with little or no shrinkage. The addition of solvent to a plastisol for reduction of viscosity is common practice, particularly for coatings applications. This mixture is referred to as an organosol. PA1 The resin ingredient is polyvinyl chloride, or a vinyl chloride copolymer, e.g., a vinyl chloride--vinyl acetate copolymer. Unplasticised polyvinyl chloride is a rigid polymer. A variety of plasticizers may be used. The type and amount will affect (modify) the plastisol viscosity and processing characteristics as well as the flexibility and properties of the finished article. Flexibility normally ranges from semirigid to soft and pliable, although, through modification with other polymers as well as through special processing techniques, the range of properties may be extended to include rigid forms. At high plasticizer levels plastisols exhibit high elongation, softness, desirable "hand" or "feel" and good abrasion resistance. Typical examples are doll parts and vinyl upholstery. As plasticizer content is reduced, flexibility and elongation decrease, and hardness, tensile strength and abrasion resistance increase. Typical examples are floor coverings and tool handles.
Handbook of Polyvinyl Chloride Formulating, .sctn. 2.3.4 at p. 35 (Edward J. Wickson ed., John Wiley & Sons 1993).
It should be noted that this broad definition of plastisol encompasses both "foamed" and "non-foamed" (or "unfoamed") variants of plastisol.
Well-known prior art texts also describe polyvinyl chloride ("PVC") plastisol and its various forms, with one such description being as follows:
Adapted from Plastisols and Organosols, (Harold A. Sarvetnick ed., Van Nostrand Reinhold Co. 1972).
There are several broad groups or forms of materials made from plastisol, namely, plastics, foams, coatings, and adhesives.
The well-known plastic form of plastisol includes a variety of products that may be cast (injection molded), rotational molded ("roto-molded"), slush molded, or dip molded. Examples of such plastic plastisol products include toys, printing plates, floor mats, fishing lures, inflatable balls, traffic cones, automobile arm rests, waterproof boots for the foot, etc.
The well-known foam form of plastisol ("foamed plastisol") can be used to make products such as athletic padding, mats, life preservers, boat bumpers, automobile gaskets, automobile body insulation, inner soles for use in footwear, etc.
The well-known coating form of plastisol is used for coating upholstery, clothing, gloves, shoes, tents, and film as well as for floor coverings and carpet backing.
A broad range of adhesives are made from plastisol. Such adhesives are used as automobile undercoatings, seam sealers, and for bonding vinyl to fabric.
Additionally, various types of earplugs, earpieces, and ear cushions for earphones and other audio devices, such as hearing aids, are well known. Some of the better prior art earplugs on the market are made from foamed plastisol, such as the earplugs described in Gardner, Jr., U.S. Pat. No. Re. 29,478 (reissued Dec. 6, 1977). However, these prior art earplugs are inferior in that comfort is compromised in exchange for effective sound attenuation or vice-versa. The result of this compromise is either that the earplugs have inferior sound attenuation quality or else are uncomfortable, in which case the user wears them incorrectly or avoids wearing them completely, thereby defeating the sound attenuation and safety purpose of using the earplugs.
Prior art earplugs are also unhygienic. A problem associated with many prior art earplugs is the requirement that they be "rolled down" or compressed to a smaller diameter by the earplug user before insertion into his or her ear canal. This compression of prior art earplugs is necessary so that a sealingly tight fit can be obtained between the earplug and the user's ear canal as the earplug subsequently expands, thereby sealingly protecting the user's ear, by sound attenuation, from injury that would otherwise occur due to excessively loud sound noise. Because the workplace can be an unsanitary environment, the repeated use of roll-down earplugs inherently gives rise to opportunities for unsanitary conditions in which any contamination on an earplug user's hands is then transferred to the user's ears as the earplugs are compressingly "rolled down" and then inserted into the his or her ears. Prior art foamed plastisol earplugs, such as those described, for example, in Gardner, Jr., U.S. Pat. No. Re. 29,478 (reissued Dec. 6, 1977), are also susceptible to absorbing liquids and to picking up foreign matter because they are sponge-like in nature. This can lead to adverse health situations caused by irritation or sensitizing of the thin layer of skin that forms the wall of the ear canal. Prior art earplugs made of latex are less than desirable because a portion of the population is allergic to latex. Other materials used in making prior art earplugs tends to be relatively harder than prior art latex or foamed plastisol earplugs, thereby causing the ear canal to become irritated with repeated insertion and extraction of the earplugs.
Many prior art earpieces subject the user's concha and ear canal to a slightly tacky or abrasive surface that, in the case of foam earpieces, is also absorbent. The epidermal permeability barrier in the ear and ear canal is easily compromised by repeated insertion and extraction of a tacky or abrasive object which, by the nature of its surface, tends to wear away the stratum corneum. Earpieces having curved flanges or skirts are also less than desirable because they are constructed in a way that allows the sharp edge of the flange or skirt to scrape against the concha and ear canal walls when extracted. Foam earpieces are doubly-damaging to the epidermal permeability barrier because their absorbent properties may tend to encourage transepidermal water loss from the basal or germinative layer of the epidermis, thereby causing dry skin in the ear canal and concha immediately adjacent to the ear canal. Degradation of the epidermal permeability barrier can result in discomfort and, in some cases, inflammation of the concha or ear canal.
It is therefore desirable to have an improved earplug or earpiece that is hygienic and that is sufficiently comfortable to be worn for extended periods without discomfort.